Steam oxidation of heat exchanger tubing is of growing interest as increasing the efficiencies of conventional pulverised fuel fired power plants requires higher steam temperatures and pressures. These new, more severe steam conditions result in faster steam oxidation reactions, which can significantly reduce the lifetime of boiler components. This paper reports some results from an investigation into the impact of steam flow rates and sample orientation on the steam oxidation of surface ground superheater tube materials. The results show that an increased steam flow rate not only causes faster oxidation rates but also a change in oxide scale morphology. In case of T23, it triggers formation of micro-layered inner oxide, whereas for T92 it promotes the formation of an outer haematite layer. For austenitic steels, the faster steam flow increases the formation of initially protective oxide scales, but also accelerates the growth of oxide nodules with prolonged exposure times.